1. Field of the Invention
The device for monitoring the operating conditions of a rolling bearing according to the present invention is used to judge the lubrication of a rolling bearing operating slightly lubricated such as rolling bearing for bearing the main spindle of machine tool.
2. Description of the Related Art
The main spindle of machine tools rotates at a high speed while being hold by a rolling bearing such as ball bearing and roller bearing. In operation, such a rolling bearing is slightly lubricated with an oil air, oil mist or the like to minimize the revolution resistance and its fluctuation. In the case of lubrication with grease, the enclosed amount of grease is minimized. In other words, the interior of the aforementioned rolling bearing is supplied with a lubricant in a minimum required amount. Accordingly, when a lubricator such a soil air supplier is out of order or the grease is exhausted, causing defective lubrication, it is likely that a severe damage such as seizing can occur in a short period of time.
It has thus been practiced to obtain data for maintenance of the aforementioned rolling bearing by detecting vibration or noise generated on the site at which the aforementioned rolling bearing is installed or temperature of this site or measuring the operating time of machine tools in which the aforementioned rolling bearing is incorporated.
Since the aforementioned data such as vibration, noise and temperature vary after the occurrence of some damage due to defective lubrication, damage on the rolling bearing cannot be necessarily prevented sufficiently. Further, the measurement of the operating time cannot cope with defective lubrication due to trouble of lubricator.
Taking into account these problems, it is desired to realize a monitor which can detect the occurrence of actual defective lubrication before the occurrence of damage due to defective lubrication.
On the other hand, as the rolling elements constituting the rolling bearing for bearing the high rotation main spindle to be incorporated in various machine tools such as machining center there are occasionally used rolling elements made of ceramics such as silicon nitride. The reason why such a rolling element made of ceramics is used is that the rolling element made of ceramics has a light weight, a small thermal expansion (small linear expansion coefficient) and excellent resistance to abrasion and seizing. However, since the rolling element made of ceramics differs from ordinary rolling bearings made of bearing steel in characteristics, the method for monitoring the abnormality thereof needs to be considered accordingly.